Originally Posted by Aquamist
Pulse width modulation type:
(Optimum operating frequency range: 30-80Hz)
This type of system resembles the modern automotive fuel injection system. The system can also be controlled by a third party EMS with a spare PWM channel. Delivery rate can either be mapped or mirroring the fuel injector duty cycle. The latter makes tuning very simple.
The valve behaves similar to an on/off gated button on a garden hose. The longer the gate is opened, the more the flow (duration). Alternative, rapid opening/shutting the gate per second (frequency) also control the flow. The common EMS uses duration for load change and frequency for RPM change. The dynamic flow range is extremely wide, 100:1 is normal.
A WAI valve should closely match the closing and shutting characteristic of a fuel injector. This is important for fuel flow mirroring algorithm since the modern EMS has a correction stage to compensate the opening delay and shutting delay.
Has this approach been tested to verify that an equal amount of water/alcohol gets into each cylinder when it's operating at (for example) 50% duty cycle?
I ask because the operating frequency of the valve shown above is in the range of the intake valves for each cylinder at the RPMs that we're concerned with. For example, suppose the valve is operating at 80hz - that's the frequency of crankshaft revolutions at 4800 RPM. So if the water injection valve is operating at 50% duty cycle (open 50% of the time) and located close to the intake manifold, it seems like there's a very real possibility of spraying water in pulses that are timed perfectly to be delivered entirely to two cylinders, while completely starving the other two.
How far away from the manifold does the jet need to be placed to ensure even distribution of water over time?